where \(\mathbf {b}\)  is the impact parameter.
As shown in [1]}, [2]}, in this space the 1 loop amplitude is expected to exponentiate into an eikonal phase, as:
\(i\tilde{\mathcal {M}}(\mathbf {b})\approx 2(s-m^2)\biggl [e^{i(\chi _1+\chi _2)}-1\biggr ]\ ,\) 
